1. Technical Field
The invention relates to pneumatic tire, and in particular to radial ply tires primarily for use with passenger and light truck vehicles. More particularly, the invention relates to such a pneumatic tire having a body ply carcass formed of at least three ply layers which turn-up about the bead area to a specific height with respect to the tire section height with two of the body ply layers having equal axial lengths.
2. Background Information
One of the main elements of a pneumatic radial ply tire construction is the body carcass which generally includes one or more body plies or ply layers formed of various textile fibers calendered within a skim coat of an elastomeric material. These body ply layers extend axially across the tire from one bead area to the other throughout the sidewall and under the tread area with the terminal ends of the body ply layers being turned-up about the beads either from the inside to the outside or visa versa and terminating at various locations along the sidewall of the tire. These body ply layers provide strength and stiffening to the sidewalls, especially during low inflation performance.
Many pneumatic tire constructions use a three body ply arrangement which utilizes three fully bead-tied-in-body plies wherein two of the ply layers are fully bead-tied-in with the remaining ply being a floating ply, that is, having its inner end not fully wrapped around the bead core. Although this ply layer arrangement has proven satisfactory, it is believed that the wrap around tie-in feature of three ply layers makes for a stronger tire construction than that of the prior three ply constructions wherein, one of the plies is not fully wrapped around the bead core.
Other tire constructions have been developed in which three body plies are wrapped around the bead core, such as shown in U.S. Pat. No. 4,366,851. However, in this construction the three body ply layers are of different lengths which increases the cost of tire manufacture by requiring an additional ply length which must be manufactured, stored and transported, as well as modifications to the tire building machines which must apply the three different axial lengths of the body ply layers to the tire building drum.
Thus the need exists for an improved pneumatic tire construction which uses at least three body ply layers which are turned-up about the bead area wherein at least two of the ply layers are of the same axial length to reduce manufacturing costs associated with the building of such a three body ply pneumatic tire.